The present invention relates to a technique for application, via a nozzle, of fluid materials in a controlled manner. More particularly, the invention relates to a nozzle for the application of a sealant or a glue, e.g. onto the joints of car bodies.
In assemblies comprising sheet metal work, there will typically be joints. These joints will occur e.g. where two or more pieces of sheet metal are joined with a certain overlap. Various techniques for joining sheet metal components are e.g. welding, riveting or gluing. For various reasons, not least cost reasons, spot welding is often used. This means that the sheets are joined by discrete spot welds, spaced along the joint. The joint then achieved, in the form of spot welds, will thus exhibit a certain similarity to a riveted seam or joint. Overlapping joints between plates joined together could provide a source of corrosion damage, as moisture might be drawn into the joint by capillary forces. Consequently, is often desirable to seal the joint with some water-resistant material, especially for sheet metal constructions to be used in outdoor applications.
A typical example where the above technique is utilised, is the design of car bodies. A car body typically consists of a multitude of sheet metal parts, joined through spot welding. Most of these joints between such sheet metal parts are, in the finished car, hidden from view behind panels, seats, etc. In order to protect these joints from corrosion caused by e.g. condensation, a sealant is usually applied onto the overlapping joint. Similar to the welding itself, the sealant application is normally performed by robots, spraying on the sealant through nozzles. The robot will follow the welded seam and apply sealant onto the joint, and it is desirable for the sealant to cover the joint with an overlap that is appropriate for the application. There is however no need for applying any sealant far beside the joint.
An important factor when applying the sealant is how well the robot can follow edges and bends in the joint; a car does not consist of many straight weld joints. This may be achieved by the robot following a predetermined, computer-stored movement pattern, corresponding to the layout of the weld seams of the body. One problem with such a technique is, however, that the dimensional accuracy in a car body is typically a couple of millimeters. Thus, a certain flexibility is demanded of the robot, and especially of its nozzle, allowing a satisfactory application of the sealant onto the joint, in spite of the nozzle being somewhat closer to, or somewhat further away from, the joint than assumed by the robot. Another way of resolving the problem of making the robot follow the weld seams is to provide it with a distance sensor in association with the nozzle, or alternatively, with some type of sensing means, trailing the sheet metal and thus sensing the actual distance from the robot nozzle to the joint. Such systems may however have other disadvantages, such as a higher cost, but also by occupying space in the robot head.
FIG. 1 illustrates a prior art nozzle, used for the application of sealant onto sheet metal joints. The nozzle is characterised by its aperture being a slot in a curved portion. As is also illustrated in the figure, the material supplied via the nozzle passage will leave the slot in a generally radial direction, from the core portion. The material will thus be sprayed in a flat cone configuration, which is also a common denomination for this type of nozzle (flat cone). This spraying technique will provide a relatively even thickness of sealant material over the joint portion. The thickness as well as the width of the applied sealant material will however be directly dependent on the distance between the nozzle and the substrate; a longer distance will provide a thinner coating over a wider area. Should the application distance increase above a certain value, the jet might be split into smaller jets in an uncontrolled manner.
Another type of prior art nozzle is shown in FIG. 2. This nozzle is similar to that of oil burners and has an interior chamber where a vortex is formed when the material is extruded. The nozzle opening may also be threaded, in order to enhance the vortex movement. When the material is ejected, the jet will have the form of a hollow cone or comet, as illustrated in the figure. As the jet is conical, this nozzle exhibits the same distance sensitivity as the nozzle discussed in connection with FIG. 1. Furthermore, as the nozzle is passed along a joint, the coating will be thicker along the sides than in the middle, where the material is best needed.
The object of the present invention is to provide a nozzle overcoming the described disadvantages of the prior art. More particularly, it is an object of the present invention to provide a nozzle for application of a coating, e.g. a sealant, so constituted as to be less sensitive to the distance between said nozzle and the surface onto which the coating is to be applied, than prior art nozzles. It is a further object of the present invention to provide a nozzle that is functioning to distribute the material, over the application surface covered, in such a way that an improved sealing is provided with a given amount of material, compared to the prior art.
The present invention relates to a nozzle, intended for the application of fluid materials, which at a front end thereof has an aperture which opens into a slot. A central portion of said slot is intended to release most of the material straight ahead. Furthermore, the slot has side portions functioning to release material in sideways directions. In a preferred embodiment, said front end is shaped like a truncated cone with a flat top, in which said slot is formed. The slot will thus be divided into three portions, with the central portion in the flat top and the angle of the side portions defined by the top angle of said cone. The nozzle is provided with a through passage from its rear end up to the slotted aperture, allowing a material under pressure to be forced through the nozzle from its rear end and out through its slotted aperture.
The three-part profile of the aperture causes the material jet forced out through the nozzle to want to split into three smaller jets. If the pressure of the material lies below a certain level, the jets will, however, be kept together by the surface tension, despite the corners between the side portions and the central portion. Dependent upon the material to be used and the reological properties thereof, different spraying pressures and angles are suitable. Most of the material is ejected through the central portion, which is open in the same direction as said through passage, whereby said surface tension primarily causes the two smaller side jets to be deflected towards the centre jet. As a consequence, the jet will have a comparatively even width over a prolonged distance, providing a wide useful application distance range. As most of the material is extruded through the central portion, the coating profile will furthermore have the greatest thickness at the centre, i.e. at the joint where the material is required.